Field of the Invention
The invention relates to a security element which can have the form of strips or patches and which is used in connection with banknotes, official and unofficial documents like passports, ID-cards, bank and credit cards, checks, paper, coupons vouchers, tickets, packages or the like. Provision of the mentioned documents with the security element improves the protection against forgery.
Description of the Related Art
Security elements typically have different characteristics which may be recognized by visual inspection, such as colour changes, holographic pictures, characters, patterns, which may particularly develop a different appearance according to the angle and direction of the observation with the naked eye. This allows a quick and reliable detection of forgery without requiring any equipment. Therefore, observable effects shall be made prominent in occurrence, so that a missing optical effect is quickly recognized to quickly identify a forgery. Of course, the security element shall be very difficult—if not impossible—to copy, to reduce the potential of forgery.
In addition, security elements may contain characteristics adapted to be recognized by machines. Such characteristics are preferably invisibly provided in the security element, so that forgery of these characteristics is impeded. Magnetic codes based on different coercivity, patterns or the like are typical examples for such characteristics, however optical characteristics with invisible rays (e.g. UV- or IR light) may be used as such characteristics.
EP 1 467 873 B1 describes a method for manufacturing a substrate which is to be used as a security element. The manufacturing process includes the formation of a metallic layer on a first side of a transparent polymeric film. A resist layer made from a darkly coloured resist is then applied on the metallic layer, the resist layer forming areas on the metallic layer which are covered by the resists and areas on the metallic layer which are not covered by the resist and the metallic layer is exposed. Then, the metal is removed for the areas which are not covered by the resist by a demetallising process, so as to demetallised regions. Then a further layer of a polymeric liquid crystal material is applied on the resist layer and the demetallised regions. The layer of polymeric liquid crystal material is optically active and develops a colour change or colour shift depending on the angle of observation. Because the metallic layer is covered with the dark coloured resist layer in the metallic areas, the colour shift effect of the polymeric liquid crystal material is clearly visible in reflected light. On the other hand, the demetallised regions are clearly distinguishable from the metallic areas in transmitted light. In the known manufacturing method, the various layers are piled one upon the other on one side of the transparent film.